Telegraphy is a technique used to transmit messages. In this way, you learn in one place what someone in another place wants to say. The device for this is a telegraph, and anyone who uses it is a telegraphist.
Telegraphy was invented over a hundred years ago. It made the transmission of messages much faster. This was not only important for newspapers and other news, but also for armies, railways and many other companies. Today, however, people hardly use telegraphy any more because of the telephone and the internet.
The word telegraphy has Greek words in it. Translated, telegraphy means "telex". That's what people still call the message they receive today: a telegram. People telegraphed in different ways. The best known was the way of sending electricity over wires. That's why radio was later called "wireless telegraphy".